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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

402

becomes intense brown, a black precipitate also forming in some cases.
Even with mixtures containing i% of cottonseed oil a feeble brown colora-
tion appears after 5-10 minutes of heating, whilst with oils and fats free
from cottonseed oil no sensible coloration is ever formed.

2.  Milliau's Reaction, modified by Tortelli and Ruggeri.—The
liquid fatty acids are extracted from 20 grams of the oil by Tortelli and
Ruggeri's lead-salt method (see General Methods, 18, i) and 5 c.c. of them
dissolved in a test-tube in 10 c.c. of 90% alcohol (puriss.), the solution being
thoroughly mixed with i c.c. of 5% aqueous silver nitrate solution and
heated in a water-bath at 70-80°.

With pure cottonseed oil the liquid assumes almost immediately a
reddish coloration which soon turns to reddish-brown, the liquid then becom-
ing turbid and appearing violet-blue in transmitted light; this happens
after 5-10 minutes heating. With oils and fats quite free from cottonseed
oil no coloration is obtained even after heating for half an hour. With
mixtures containing only i% of cottonseed oil, a deep brown colour soon
appears.

3.  Halphen's Reaction.—According to  the most recent statement
by the author,1 this test is carried out as follows : In a test-tube are placed
i  c.c.   of.the oil and 2  c.c.   of   sulphocarbon   reagent   prepared  by
dissolving1*! gram of powdered, refined sulphur in 100 c.c. of carbon disul-
phide and then diluting with 100 c.c. of amyl alcohol.    The tube is immersed
to the extent of two-thirds in a salt solution and heated to boiling for an
hour, 2 c.c. of the same reagent being then added and the heating continued
for 30-40 minutes.   In presence of cottonseed oil, a red, pink or orange-
pink coloration—according to the proportion of cottonseed oil present
(down to about i% as a minimum)—appears more or less rapidly.

Water hinders the reaction, so that the test-tube should be thoroughly dry
and the reagents and oil anhydrous ; the latter is filtered through a double
dry filter.

Some cottonseed oils which have undergone special treatments give, in
place of a decided red coloration, a brown tint with an orange basis, this being
well seen by looking through the whole depth of the liquid at a white ground.

With green or greenish olive oils containing little cottonseed oil, the reaction
is uncertain ; in such cases it is well to decolorise the oil beforehand by heating
it at about 50° with animarcharcoal and filtering at the same temperature.

4.  Halphen's Reaction, modified by Gastaldi.—A test-tube con-
taining 5 c.c. of the oil, i drop of pyridine and 4 c.c. of a i% solution of
sulphur in carbon disulphide is heated in a boiling water-bath for about
30-60 minutes.   In presence of cottonseed oil a red, pink or yellowish-pink
coloration—according to the amount of the cottonseed oil—is formed as
with Halphen's reagent; the colour is more distinct and intense than with
the latter and is visible even with 0-5% of cottonseed oil.

*
* *

Halphen's reaction and Gastaldi's modification of it fail with cottonseed
oils which have been heated above 200° or subjected to prolonged treatment

1 G. Halphen :   Huiles et Graisses

'.es comestibles (Paris,  1912), p. 340.tash, heated for an hour in a reflux apparatus and